Process for producing fiber or pulp



Patented Nov. 8, 1932 UNITED STATES PATENT OFFICE HENRY STINSON HOOPER,OF OLD TOWN, MAINE, ASSIGNOR TO PENOBSCOT CHEMICAL FIBRE COMPANY, ACOBPORATION'OF MAINE PROCESS FOR PRODUCING FIBER OB BUT-P No Drawing.

The ivention relates to a digesting or cooking process of treating'woodchips for the purpose of producing fiber or pulp, said process toconsist of morethan one stage.

The usual practice in the productionbf fibrous pulp from deciduous woodsby the soda process is to fill a digester with wood chips then 'add aquantity of caustic soda, sodium hydroxide, in aqueous solution, equalto about 25% of the dry weight of the chips, to raise this charge to atemperature of about 340 F. and a pressure of approximately 110 lbs. andto hold it at this temperature for from 4' to 6 hours .and then todischarge the digested mixture to washing pans. This is a very drastictreatment which results in the solution of a substantial percentage ofthe cellulosic fiber and its loss so far as its value as pulp isconcerned. Moreover, the comparatively expensive chemical, sodiumhydroixide is used throughout the digesting perio The sulphate process,which is appli-- cable to deciduous woods although more generally usedwith coniferous woods, differs from the soda process in utilizing amixture of caustic soda and sodium sulphide as a digesting agent insteadof'caustic soda alone. This process as heretofore practiced is equallysubject to the disadvantages above pointed out inv connection with thesoda process.

The purpose of my invention is to produce cellulosic fiber from woods bya process in more than one stage. In treating deciduous woods, forexample, I use a comparatively cheap chemical, sodium carbonate, in weaksolution in the first stage, and in'the second stage a solution ofcaustic soda which is weaker than that now commonly used in the sodaprocess. By so doing, it is possible to obtain a larger yield of pulp,from' one to five per cent, and a greater economy in the use ofchemicals, than has been possible by the usual methodof using causticsoda only.

I The same advantages can be obtained in the sulphate process by usingin a first stage a solution containing sodium carbonate instead ofcaustic soda and in the second stage a solution containing less causticApplication'filed February 10, 1931. Serial No. 514,913.

soda and less sodium sulphide than has hitherto been considerednecessary.

The following illustrates a preferred way in which to carry out myprocess on deciduous woods. The first stage is initiated by filling adigester with'chips equal to 12,500 lbs. of dry wood and adding 2500gallons of an aqueous solution containing 1250 lbs. of sodium carbonate.Steam is admitted to the digester and its charge is brought to about 110lbs. per square inch gauge pressure (not over 125 lbs.), and atemperature of approximately 330 F. and is held at this temperature from30to minutes. At such temperatures, acids tend to be freely formed. Thesodium carbonate present effects the neutralization of these acids andthe generation of carbon dioxide gas, CO This CO is permitted to escapetogether with some steam through a relief Valve at the' top of thedigester. This removal of the 00 or the greater portion thereof,prevents it fromcombining detrimentally with the caustic soda pumped inat the beginning of the second stage of the process.

At the end of the first stage of the process the admission of steam 'tothe digester is stopped.

To initiate the second stage of the process, 2750 gallons of ,a solutioncontaining 1900 lbs. of caustic soda is pumped in. To facilitate this,the pressurein the digester may be lowered slightly, as by 10 or- 15lbs. on the gauge.

. Steam is again admitted and the pressure in the digester brought-toabout 110 lbs. and the temperature of the charge to approxi mately 340F. This temperature is maintained for about-4 hours.- At the end of thisperiod, the admission of steam is stopped and the contents of thedigester blown out into a suitable receiving vessel. Y

During the process a vigorous circulation of the liquid contents of thedigester is main- 'digester as far as is practical by pumping,

known methods. When my process 1s practiced .in more than two stages,this removal of the spent liquor may take place between any two stages.When the spent liquor is drawn out of the digester after treating thematerial in the sodium carbonate solution, it is in such a-conditionthat the by-products may be easily recovered, that is, more easily thanin the case of the spent liquor removed at the end of the ordinary sodaprocess. Moreover, when the liquor is removed prior to the final stageof the digestion, the bleaching of the product is facilitated. However,the removal of the liquor between stages of the process is not necessaryto the successful production of pulp by this invention.

My invention is equally applicable as an improvement in the digestion ofwoody material by the sulphate process. In this case, the first stage iscarried on with a solution of sodium carbonate in the proportionateamount above set forth, namely about 10 to 12% of the dry weight of thechips, if wood be the material treated. The CO is permitted to escape asabove. After the first stage of the digestion is completed, a solutioncontaining about 10% of the dry weight of the chips of caustic soda andabout 6% of the same weight of sodium sulphide is pumped into thedigester. The second stage is completed substantially as in the presentpractice of the sulphate process.

Whereas I have described in detail methods of carrying out my process. Ido not confine myself to these particular details, as it is possible toincrease the number of-stages and to vary the percentages of,chemical;time of digestion and temperature to correspond with the difi'erenttypes of woody material being treated or to obtain different grades ofcellulosic fiber.

Having thus described my process I claim:

1. The process of producing fiber orpulp from wood which consists offirst cooking wood chips in a sodium carbonate solution at a temperatureof about 330 F. for about .to 1 hour, while permitting the escape of COformed, then adding a stronger solution 'con-.

taining sodium hydroxide and maintaining this charge ata temperature ofabout 340 F. for 2 to 4 hours.

2. The process of producing fiber or pulp by a multi-stage cookingprocess comprising a first stage in which wood chips are cooked in asodium carbonate solution suificientin amount and for a suflicient timeand at such temperature as to neutralize substantially all acids formedwith the generation and emission of CO and a later stage in which thechips are cooked ina sodium hydroxide so lution sufiicient in amountand. for such time and at such temperature as to'reduce the wood topulp. Y

3. Process of producing fiber or pulp by multi-stage cooking processcomprising a first stage in which the raw material is cooked in a sodiumcarbonate solution suflicient in amount and for a sufficient time and atsuch temperature as to neutralize substantially all acids formed withthe generation and emission of CO and a later stage in which thematerial is cooked in a solution of sodium hydroxide and sodium sulfide,sufiicient in amount and for such time and at such temperature as todissolve substantially all the constituents of the material except thecellulosic fiber.

4. A process of producing paper pulp from wood chips which consists of atwo stage cooking process, using in the first stage a solutioncontaining sodium carbonate equivalent to from 8 to 12% of the dryweight of the chips and raising this to to 125 lbs. steam pressure andmaintaining this pressure for to 1 hour or more while permitting theescape of the CO2 formed, and using in the second stage a solution ofsodium hydroxide equivalent to 15% to 20% of the dry weight of the wood,raising the pressure to 80 to 110 lbs., and holding it there for 2 or 4hours or until the cook is completed.

5. A process of producing paper pulp from cellulose material whichconsists of a two stage cooking process, using in the first stage asolution containing sodium carbonate equivalent to from 8 to 12% of thedry weight of the chips, raising this mixture to from 80 to 125 lbs.steam pressure and maintaining this pressurefor to 1 hour or more, whilepermitting the escape of the CO formed, and using in the second stage asolution of sodium hydroxide equivalent to 8 to 12% of the dry wei ht ofthe wood, and sodium sulphide equivalent to 4 to 8% of the dry weight ofthe wood, raising the pressure to 80 to 110 lbs. steam pressure, andholding it there for from 2 to :4 hours or until the cook is completed.

, 6. The. process of producing paper pulp from wood which consists offirst digesting wood chips for 30 to 60 minutes in a solution containingan amount of sodium carbonate equal to approximately 10% of the dryweight of the wood, at a steam pressure of about 110 lbs. per squareinch, while permitting the escape of the CO formed, then adding astronger solutio containing an amount of sodium hydroxide e ual toapproximately 15% of the dry weight of the wood and digesting the chipsat a steam pressure of about 110 lbs. per square inch for about 4 hours,or until substantially all the constituents of the wood except thecellulose fibers are dissolved.

7. The process of producing paper pulp from wood which consists of firstcooking wood chips for 30 to 60 minutes with a solution containing anamount of soduim carbonate equal to approximately 10% of the dry weightof the wood, at a steam pressure of about 110 lbs. per square inch,while permitting the escape of the CO formed, then adding a solutioncontaining an amount of sodium hydroxide equal to approximately of thedry weight of the wood, and

10 sodium sulphide equal to approximately 6% of the dry weight of thewood, and cooking the mixture at a steam pressure of about 110 lbs. persquare inch for about 4: hours or until the cook is completed.

8. The process of producing pulp from wood chips by a multi-stagecooking process comprising a first stage in which the wood chips aredigested in a sodium carbonate solution of suflicient strength and for asuflicient time and at such temperature as to neutralize substantiallyall acids formed with the generation and emission of CO ,-and a laterstage in which the wood is digested in a stronger solution containingsodium hydroxide, of

suficient strength and for such time and at such temperature as todissolve substantially all constituents of the wood except the cellulosefiber.

v 9. The process of treating cellulosic material, comprising first amild digestion of the material in a sodium carbonate solution, removalof the spent liquor from the digester upon the completion of this stageof the process, treatment of such liquor for the re- 85 covery oforganic by-products, and subseent digestion of the material in astronger s lution containing sodium hydroxide until the material isreduced to pulp.

IO. The process of producing pulp from wood chips by a multi-stagecooking process which comprises digesting the chips in a sodiumcarbonate solution with the application of heat and at a pressure inexcess of 80 pounds'per square inch, drawing off the spent liquor, anddigesting the remaining material in a solution containingsodiumhydroxide at a pressure in excess of 80 pounds per square inchuntil the material is substantially reduced to pulp.

HENRY STINSON HOOPER.

